The present invention concerns a method and apparatus for testing for the volume of a hollow body, for testing the tightness of a hollow body and for detecting a change in volume caused by pressure stress applied to walls of the hollow body, namely, for example, testing flexible hollow bodies such as coffee packages.
In the packaging of certain foodstuffs, such as sweeteners and coffee or medications such as effervescent tablets, it is essential that packaging containers are sealed tightly against the environment in order to prevent the packaged goods from becoming contaminated, for example, by atmospheric humidity. The goods are sometimes packed in containers such as bottles, cans or pouches. These containers are generally dimensionally stable or flexible hollow bodies which are fitted with lids or closable sections which can be opened, but which in the closed state are intended to tightly seal the interior of the hollow body.
Various procedures, for example, welding, are used in the manufacture of such containers. In addition to the tightness of such hollow bodies, also the rigidity of the walls of dimensionally stable containers, especially in the area of junction points, is an essential criterion determining their usability. Excessively rigid or excessively weak sections, such as weld seams may result in cracks forming when the container is in use, for example, in areas where parts of different rigidity are joined.